1. Field of the Invention
The present invention relates to a composition for a resist underlayer film effective for a multilayer resist process used for microfabrication in a process for manufacturing semiconductor devices and the like, a process for forming a resist underlayer film using the same, a resist patterning process using the underlayer film composition suitable for exposure by deep ultraviolet ray, KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), F2 laser light (157 nm), Kr2 laser light (146 nm), Ar2 laser light (126 nm), soft X ray (EUV), an electron beam (EB), an ion beam, X ray and the like, and a fullerene derivative useful in these technical fields.
2. Description of the Related Art
As higher integration and higher speed of LSI are realized, finer pattern size is achieved rapidly. Along with the achievement of finer pattern size, the lithography techniques have accomplished micropatterning by using light sources with shorter wavelength and properly selecting resist compositions corresponding to the light sources. As for such compositions, positive photoresist composition's used as a monolayer are mainly selected. Each of these monolayer positive photoresist compositions has a skeleton providing an etching resistance against dry etching with chlorine-based gas plasma or fluorine-based gas plasma in the resist resin, and has resist mechanism that an exposed area turns soluble, thereby forming a pattern by dissolving the exposed area and dry etching a substrate to be processed to which the resist composition is applied by using the remained resist pattern as an etching mask.
However, when a pattern is rendered finer, that is, a pattern width is rendered narrower, without changing the thickness of a photoresist film to be used, resolution performance of the photoresist film is deteriorated. In addition, developing the pattern of the photoresist film with a developer causes a pattern collapse because a so-called aspect ratio of the pattern becomes too high. Therefore, the thickness of a photoresist film has been made thinner along with achieving a finer pattern.
On the other hand, for processing a substrate to be processed, a method to process the substrate by dry etching by using a pattern-formed photoresist film as an etching mask is usually used. Actually however, there is no dry etching method capable of providing an absolute etching selectivity between the photoresist film and the substrate to be processed. Therefore, the resist film is also damaged and collapsed during processing the substrate, so that the resist pattern cannot be transferred to the substrate to be processed correctly. Accordingly, as a pattern becomes finer, it has been required that a resist composition has a higher dry etching resistance.
In addition, the use of shorter wavelength exposure radiations has required resins used for photoresist compositions to have low light-absorbance at the wavelength to be used. Accordingly, as the radiation shifts from i-line to KrF and to ArF, the resin shifts from novolac resins to polyhydroxystyrene, and to resins having an aliphatic polycyclic skeleton. Along with this shift, an etching rate of the resin actually becomes higher under the dry etching conditions mentioned above, and recent photoresist compositions having a high resolution tend to have a low etching resistance.
As a result, a substrate to be processed has to be dry etched with a thinner photoresist film having lower etching resistance. The need to provide a material for this process and the process itself has become urgent.
A multilayer resist process is one of solutions for these problems. This method is as follows: an intermediate film having a different etching selectivity from a photoresist film, that is, a resist upperlayer film, is set between the resist upperlayer film and a substrate to be processed to obtain a pattern in the resist upperlayer film; the pattern is transferred to the intermediate film by dry etching by using the upperlayer resist pattern as a dry etching mask; and then the pattern is transferred to the substrate to be processed by dry etching by using the intermediate film as a dry etching mask.
In one example of a two-layer resist process, which is one of the multilayer resist processes, a silicon-containing resin is used for the upperlayer resist composition and an organic resin having a high carbon content such as a novolac resin is used for the underlayer film. The silicon resin has a good etching resistance to a reactive dry etching using oxygen plasma, while it is easily removed by etching using fluorine-based gas plasma. On the other hand, the novolac resin is easily removed by a reactive dry etching using oxygen plasma, while it has a good etching resistance to dry etching using fluorine-based gas plasma or chlorine-based gas plasma. In this example, a novolac resin film as a resist intermediate film is formed on a substrate to be processed and a resist upperlayer film using a silicon-containing resin is formed on the resist intermediate film. Then, a pattern is formed in the silicon-containing resist film by irradiation of an energy beam and sequential aftertreatment such as development; part of the novolac resin, on which the resist pattern is removed, is removed by a reactive dry etching using oxygen plasma by using the pattern-formed silicon-containing resist film as a dry etching mask to transfer the pattern to the novolac film; and thereafter, the pattern can be transferred to the substrate to be processed by etching using fluorine-based gas plasma or chlorine-based gas plasma by using the pattern transferred to the novolac film as a dry etching mask.
In such a pattern transfer by the dry etching, when the etching resistance of the etching mask is sufficient, the transferred pattern having a relatively good profile is obtained. Thus, a problem such as a pattern collapse caused by friction and the like by a developer upon resist development hardly occurs, and a pattern having a relatively high aspect ratio can be obtained. Therefore, for example, when the resist film using the novolac resin has the thickness corresponding to the film thickness of the intermediate film, even in the fine pattern which could not be formed directly because of the pattern collapse upon development due to the aspect ratio, according to the above two-layer resist process, the novolac resin pattern having the sufficient thickness as the dry etching mask for the substrate to be processed is obtained.
The multi-layer resist process further include a three-layer resist process which can be performed by using a typical resist composition used in a monolayer resist process. For example, this method is configured to form: an organic film based on novolac or the like as a resist underlayer film on a substrate to be processed; a silicon-containing film as a resist intermediate film thereon; and a usual organic photoresist film as a resist upperlayer film thereon. Since the organic resist upperlayer film exhibits an excellent etching selectivity ratio relative to the silicon-containing resist intermediate film for dry etching by fluorine-based gas plasma, the resist pattern is transferred to the silicon-containing resist intermediate film by means of dry etching based on fluorine-based gas plasma. According to this process, as well as two-layer resist process, patterns of novolac films having sufficient dry etching resistances for processing can be obtained insofar as patterns can be transferred to silicon-containing films, even by adopting: a resist composition which is difficult to be formed with a pattern having a sufficient film thickness for direct processing of a substrate to be processed; and a resist composition having an insufficient dry etching resistance for processing of a substrate.
While numerous techniques have been known (such as Japanese Patent Laid-Open (kokai) No. 2004-205685 and the like) for the organic underlayer film as described above, accompanying decrease of processing line width, further improvement of dry etching resistance are required. Such problems that phenomena of wiggling, bending, and the like (collectively means wiggling) of a resist underlayer film are caused when the resist underlayer film is used as a mask for etching a substrate to be processed (Proc. of Symp. Dry. Process, (2005), p 11), and these problems are caused notedly especially when a finer pattern of 40 nm or less is formed. Such wiggling of a finer pattern is considered to be caused by swell of the underlayer film due to an increased volume thereof and a lowered glass transition point thereof by a phenomenon having been reported, in which hydrogen atoms of a resist underlayer film are substituted with fluorine atoms during etching of a substrate by a fluorocarbon-based gas (Proc. Of SPIE Vol. 6923, 692320, (2008)). In turn, it has been reported that the problem of wiggling can be prevented by adopting an organic material, which is low in hydrogen atom content ratio, and that the problem of dry etching resistance can be improved by adopting an organic material, which is high in carbon atom content ratio, as a resist underlayer film. In this respect, amorphous carbon films formed by CVD are each allowed to be extremely high in carbon atom content ratio and extremely less in hydrogen atom content ratio in the film itself, and are effective for having excellent dry etching resistance and prevention of wiggling. However, CVD is unfortunately insufficient in filling-up characteristic of a stepped substrate, and it is often difficult to introduce a CVD apparatus due to the problems of its high cost and an increased footprint occupation area of the apparatus. Therefore, it will be able to obtain a remarkable merit of cost reduction by simplification of a process and an apparatus, if the above problem of wiggling is solved based on a resist underlayer film composition which can be formed into a film by coating, particularly by spin coating.
As the above-described film-forming material which is high in carbon atom content ratio and low in hydrogen atom content ratio and which can be coated and formed into a film, films each containing a fullerene derivative having extremely high in carbon ratio have been proposed. For example, a method for forming a film by fullerene itself (here, fullerene is a collective term of allotropes of carbon possessing a closed shell cluster composed of many carbon atoms, is typified by C60 and C70 and includes C74, C76, C78, C82, C84, C90, C94, C99, C108 and further higher carbon clusters) was proposed at the earliest stage (Japanese Patent Laid-Open (kokai) No. H06-61138), but it was difficult to use fullerene itself because fullerene was extremely poor in solubility in a general solvent coated on a substrate. Accordingly, in Japanese Patent Laid-Open (kokai) No. 2004-264710, Japanese Patent Laid-Open (kokai) No. 2006-227391), for example, fullerene was converted to its derivative soluble in a solvent for application and the fullerene derivative was dispersed into an organic resin to obtain a cured film. However, because of the conversion of a fullerene to its derivative, a problem that the key hydrogen atom containing ratio and carbon atom containing ratio largely change has been caused. To solve that problem, in WO2008/62888, it was proposed to use a fullerene-amine adduct (aminated fullerene), which is a derivative having a possibility of generating a fullerene or a substance having a similar hydrogen atom and carbon atom containing ratio to a fullerene by heat decomposition. This technique is important in respect of maximizing the merit of using the fullerene derivative. On the other hand, in a multilayer resist process, an intermediate layer is formed on an underlayer film as appropriate, and then an upperlayer resist is formed to form a pattern, while a chemically amplified resist acting by acid catalyst reaction is used as the upperlayer resist. Therefore, when an amine base generated by heat decomposition of the fullerene derivative (fullerene-amine adduct) reaches the upper resist film even in minute amounts, it affects the acid catalyst reaction in forming the upper resist pattern to cause a so-called poisoning problem such as deterioration of a pattern profile and a development defect.